Polypropylene composition useful for making solid state oriented

Details Polypropylene composition useful for making solid state oriented Polypropylene composition useful for making solid state oriented

1998-08-18

2000-03-14

Warzel, Mark L.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

528232, C08L 2300

Patent

active

060374179

ABSTRACT:
Disclosed is a polypropylene composition useful for making solid state oriented film. The composition comprises two predominantly isotactic polypropylenes with the melting point temperature of one of the polypropylenes being substantially lower than the melting point temperature of the other. In one embodiment of the composition the higher melting point polypropylene is made by Ziegler-Natta catalysis, while the lower melting point polypropylene is made by metallocene catalysis. Compared to polypropylene with similar melt flow rate and made by Ziegler-Natta catalysis, and solid state oriented film thereof, the composition provides a better balance of elevated temperature draw characteristics and physical properties of oriented film made therefrom. Thus, at the same or lower elevated temperature yield stress, oriented film of the composition exhibits improved properties such as stiffness, elongation-at-break, dimensional stability, and oxygen barrier.
Also disclosed is a method for the manufacture of oriented, flexible packaging film. In the method a cast sheet is melt extruded from the composition, and, after cooling until it is solid, the cast sheet is stretched to the desired extent of orientation at a temperature which the sheet does not break while being stretched, but below the T.sub.m of the composition. The resulting film then is cooled to at least the crystallization temperature of the lower melting point polypropylene.

REFERENCES:
patent: 5530065 (1996-06-01), Farley et al.

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